The present invention relates to pivotable ball joints and more specifically, to pivotable compression ball joints.
There are several types of known vehicle suspension systems. A common component in these suspension systems is the ball joint. Depending on the suspension type, the ball joint may be a load-bearing ball joint in tension, a load-bearing ball joint in compression or a non-load-bearing ball joint which is also known as a stabilizing ball joint.
A suspension's ball joint is designed to provide proper vehicle steering function. Ball joints are intended to require a proper amount of torque to pivot with minimal variations. A proper amount of ball joint tightness is required for steering alignment capability and smooth steering. If the torque is too high, increased steering effort results which places an increased load on the steering system and yields poor returnability. If the torque is too low, return overshoot occurs and wheel kick results from road inputs.
Additionally, ball joints are designed so that internal wear is minimized. However, the ball joints used in vehicle suspension systems are inevitably subject to wear over time. Therefore, a convenient and a reliable method of determining when joint wear has proceeded to a point requiring replacement of the ball joint is required. Conventionally, the method used for determining when a ball joint is worn to the point of requiring replacement is to manually check for looseness in the joint. This diagnostic technique has proven to be sufficient for stabilizing ball joints which are not under an axial load. This is because the stabilizing ball joint when worn will generally contribute to looseness in the vehicle suspension in a horizontal direction. The stabilizing ball joint is typically designed so that when horizontal suspension looseness is sensed, a worn ball joint condition is properly diagnosed as the cause.
A known diagnostic technique for use with suspension ball joints which are under a vertical axial load is to support the vehicle at the suspension control arm and pry under the wheel to check for relative displacement between the wheel and the control arm. It has been found that this common method of measuring vertical looseness in the ball joint tends to lead to repeated misdiagnoses of ball joints as being in a worn condition when in fact they are still in a suitably operable condition.
For tension ball joints this misdiagnoses problem was overcome by designing a preloaded ball joint with a wear indicator. This type of prior art ball joint is illustrated in FIG. 4 and is explained in detail in U.S. Pat. No. 4,358,211 to Goodrich which is assigned to the assignee of this invention.
For the tension ball joint as shown in FIG. 4, an axial load is typically applied downward on stud 8. This axial load results in the force on head 5 being normally in a downward direction, causing the main bearing surface of the joint to be at interface 6. A preload is applied to the joint by elastomeric ring 2 which is positioned between cover 4 and upper bearing seat 3. Therefore, the preload applied to stud 8 by ring 2 is in the same direction as the tension load.
Upper bearing seat 3 includes protuberance 7 which extends outside cover 4. As wear occurs in the joint, for the most part at interface 6, elastomeric ring 9 expands to take up the space vacated by the worn metal, and protuberance 7 withdraws within cover 4. Retraction of protuberance 7 provides a method for visually determining the amount of wear that has occurred in the tension ball joint. By providing a means of visual diagnoses, misdiagnosis problems have been substantially eliminated for a suspension's preloaded tension ball joints.
In the case of compression lower ball joints however, the design and loading direction make it much more difficult to incorporate a wear indicator. With a compression lower ball joint, the compressive load that is normally applied to the joint prevents the prior art design as illustrated in FIG. 4 from operating. With a compression ball joint the compressive force is in the opposite direction of the preload force on the stud 8 of FIG. 4 and therefore, would prevent the protuberance 7 from retracting into the cover 4 properly, thereby preventing this known prior-art diagnostic mechanism from operating.
Conventional compression lower ball joints used in automotive suspensions comprise a metal ball contained within a metal socket. The ball has a stud extending therefrom through an opening in the socket wall. The socket is attached to one suspension component and the stud is attached to another thereby permitting relative pivoting movement therebetween.
This type of joint normally exhibits some looseness. If a joint is constructed too tightly, the ball joint becomes locked in position potentially interfering with joint operation and with assembly of the joint into a suspension. If the joint is too loose it will likely be found defective and replaced even though it is not worn. Because of the normal looseness associated with a non-preloaded joint, the conventional compression ball joint is susceptible to misdiagnosis as being worn-out when in fact it is still in operable condition. This leads to unnecessary ball joint replacement costs. Therefore, a compression ball joint is required that provides a positive indication of when it is worn to the point of requiring replacement.